What is the principle of insulation resistance test? What are the factors that affect the measurement?

Date：2022-09-15 16:42:44Views：1401

The insulation resistance tester calculates the insulation resistance value according to Ohm's law. Output the DC voltage far lower than the dielectric strength test, and then measure the current to calculate the insulation resistance. High voltage insulation resistance tester is a commonly used and indispensable instrument for power, post and telecommunications, communication, mechanical and electrical installation and maintenance, as well as industrial enterprise departments using electricity as industrial power or energy. It is suitable for measuring the resistance of various insulating materials and transformers, motors, cables and electrical appliances. The following is a brief analysis of insulation resistance test for your reference.

In fact, the insulation resistance is large, but not infinite, so it can be calculated by measuring the leakage current. The megger can display the resistance value of the insulation resistance. The results generally include k Ω, M Ω, G Ω, and even T Ω in some cases. The insulation resistance value directly represents the insulation quality between two conductors.

Factors Affecting the Results of Insulation Resistance Tester

The reason why the results of the insulation resistance tester will be affected is that the current value is obtained by applying a constant voltage to the tested object. These external factors, such as temperature and humidity, may seriously affect the test results

First, we will analyze the nature of the current generated during the insulation test and assume that none of these factors will affect the measurement

The total current of insulating materials when applied with voltage consists of three components: capacitive current, also called capacitive charging current

Capacitive current: When testing insulation resistance, the charging current must first fill the capacitance of the insulating material being tested This current is relatively large at the beginning of the test instant, and will drop to near zero at a fast speed once the circuit under test is charged It will become stable after a few seconds or more than ten seconds, and the current is small enough to be negligible relative to the total current

Absorption current. The absorption current is different from the capacitance current. The absorption current decreases much more slowly than the capacitance charging current. It usually takes several minutes to reach a near zero and stable data

Leakage current, also called polarization current, is a current generated in the process of polarization of insulating medium under the action of voltage. The size of current indicates the quality of insulation For motors with large capacity or cables with long distance and large cross section, it may take about 30 minutes for the cables to reduce and stabilize the capacitor charging current and absorption current, so that the insulation test can obtain a correct result.

When a steady current is applied to the circuit, the total current in the insulating material under test will change with time, which means that the insulation resistance will also change significantly with time

Influence of temperature: The value of insulation resistance will change when the temperature rises or decreases In the preventive test, the insulation resistance test must be conducted at a similar temperature. If this condition cannot be met, a reference temperature shall be set as the standard and converted for correction According to the general rule, if the temperature rises by 10 ℃, the resistance value drops to half of the resistance value at the reference temperature point; If the temperature drops by 10 ℃, the resistance is twice the reference value

The influence of humidity on the test results of the insulation resistance tester mainly depends on the turbidity of the insulator surface. However, special attention should be paid to that the insulation resistance should not be measured when the temperature drops below the dew point.

The above is the insulation resistance test related content of the wound core detection small compilation, and I hope it will be helpful to you. Our company has a team of professional engineers and industry elites, and has built three standardized laboratories with an area of more than 1800 square meters, which can undertake a variety of test projects such as electronic component test verification, IC authenticity identification, product design material selection, failure analysis, functional testing, factory incoming material inspection and tape weaving.